Localization of Rh1(D), 2(C), 3(E), 4(c), 5(e) and 25(LW) antigens of human Rh blood groups in fetal erythrocyte membranes

The fetal erythrocyte membranes were partially solubilized with Triton X-100 at the low concentration (0.5%). The localizations of Rh1(D), 2(C), 3(E), 4(c), 5(e) and 25(LW) were investigated. Using hemagglutination inhibition assay, Rh1(D) antigen activity was observed in the Triton-treated membrane (Triton shell) containing mainly band 1, 2 (spectrin), band 5 (actin), band 4.1 and a part of band 3, while Rh2(C), 3(E), 4(c), 5(e) and 25(LW) antigens were detected in the supernatant containing band 3, 6, 2.2, 2.3 and 4.2. It is suggested that: Rh1(D) antigen would associate with cytoskeleton matrix of fetal erythrocyte membranes; Rh1(D) and Rh25(LW) antigens might be integral membrane proteins, while Rh2(C), 3(E), 4(c) and 5(e) antigens would be surface membrane proteins which are easily released from membranes by EDTA, mercaptoethanol and alkaline treatments.     

Reconstitution of rhodopsin and the cGMP cascade in polymerized bilayer membranes

The successful reconstitution of rhodopsin, the rod outer segment (ROS) G protein, and the ROS phosphodiesterase (PDE) into partially polymerized bilayer membranes is described. Purified bovine rhodopsin (Rh) was inserted into performed partially polymerized lipid vesicles. Sonicated vesicles composed of approximately equal moles of dioleoylphosphatidylcholine (DOPC) (or 1-palmitoyl-2-oleoyl-phosphatidylcholine) and 1,2-bis(octadeca-2,4-dienoyl)phosphatidylcholine (DENPC) were photolyzed with 254-nm light to polymerize the DENPC and form domains of DOPC and polyDENPC in the vesicle wall. Rh-octyl glucoside (OG) micelles were slowly added to the vesicle suspension to give 15 mM OG (below the OG critical micelle concentration). The suspension was incubated and then dialyzed and purified on a sucrose gradient. Ultracentrifugation revealed a major Rh-lipid band which was harvested and found to contain a 100 +/- 10 phosphatidylcholine to rhodopsin ratio (Rh-polyDENPC/DOPC). The orientation of Rh in the membrane was determined by limited proteolytic digestion of Rh and by competitive inhibition of monoclonal antibody binding to solubilized disk membranes. Results were compared with control membranes of Rh-DOPC (1:43) prepared by insertion and Rh-phospholipid membranes prepared by detergent dialysis. Visual inspection of thermolysin proteolytic patterns of Rh indicates one major population cleaved at the carboxy terminus, as is found in disk membranes with an asymmetric arrangement of Rh. In contrast, proteolysis of a Rh-egg PC/PE (1:50/50) membrane (detergent dialysis) produced two Rh populations, which indicates a symmetric arrangement of Rh. The Rh-polyDENPC/DOPC (1:100) membranes were allowed to compete with solubilized, immobilized disk membranes for the monoclonal antibody R2-15 (specific for the amino-terminal region of Rh). They were intermediate between the asymmetric ROS disk membranes and the symmetric dialysis membranes in their ability to bind the R2-15 monoclonal antibody. The data indicate approximately 80% of the Rh's in Rh-polyDENPC/DOPC are in the normal orientation found in disks. These Rh-containing polymerized bilayer membranes demonstrated functionality as determined by chemical regeneration, kinetic spectrophotometry, and cGMP cascade reconstitution experiments. In the latter experiments the peripheral proteins, ROS G protein and PDE, bound with comparable efficiency to both the polymerized PC bilayers and egg PC bilayers. Thus the biocompatibility of the phosphatidylcholine membrane surface was maintained after polymerization of DENPC.     

Partition of catalase and its peroxidase activities in human red cell membrane: effect of ATP depletion.

Partititon of catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase EC 1.11.1.6) and peroxidase (donor:hydrogen-peroxide oxidoreductase EC 1.11.1.7) activities between the red cell membrane and the cytosol were studied under various experimental conditions. A small but significant amount of catalase (1.6%) was retained on human red cell membranes prepared by hemolysing washed red cells with 30 volumes of 10 mM Tris buffer, pH 7.4. Membrane -bound catalase had a relatively higher peroxidase activity than the soluble enzyme fraction. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate of the solubilized membranes demonstrated catalase to be a single band with a molecular weight of 60 000. Membranes prepared from adenosine triphosphate-depleted red cells depicted a two to three-fold increase in catalase activity, as well as an increase in 60 000 molecular weight band on polyacrylamide gel electrophoresis. The extra amount of retained catalase was a less efficient peroxidase than found in fresh membranes. The binding of catalase to ATP-depleted red cell membranes was dependent upon both pH and hemolysing ratio. Red cells incubated at pH 7.1 demonstrated a decrease in bound catalase, as did membranes prepared from red cells hemolysed at 1:100 dilution. beta-Mercaptoethanol decreased the catalase activity in the membranes and increased the odianisidine peroxidase activity without any significant effect on the 60 000-dalton band.     

Role of low density lipoprotein receptor-dependent and -independent sites in binding and uptake of chylomicron remnants in rat liver

The role of the low density lipoprotein (LDL) receptor in the binding of chylomicron remnants to liver membranes and in their uptake by hepatocytes was assessed using a monospecific polyclonal antibody to the LDL receptor of the rat liver. The anti-LDL receptor antibody inhibited the binding and uptake of chylomicron remnants and LDL by the poorly differentiated rat hepatoma cell HTC 7288C as completely as did unlabeled lipoproteins. The antireceptor antibody, however, decreased binding of chylomicron remnants to liver membranes from normal rats by only about 10%. This was true for intact membranes and for solubilized reconstituted membranes and with both a crude membrane fraction as well as with purified sinusoidal membranes. Further, complete removal of the LDL receptor from solubilized membranes by immunoprecipitation with antireceptor antibody only decreased remnant binding to the reconstituted supernatant by 10% compared to solubilized, nonimmunoprecipitated membranes. Treatment of rats with ethinyl estradiol induced an increase in remnant binding by liver membranes. All of the increased binding could be inhibited by the antireceptor antibody. The LDL receptor-independent remnant binding site was not EDTA sensitive and was not affected by ethinyl estradiol treatment. LDL receptor-independent remnant binding was competed for by beta-VLDL = HDLc greater than rat LDL greater than human LDL (where VLDL is very low density lipoprotein, and HDL is high density lipoprotein). There was weak and incomplete competition by apoE-free HDL, probably due to removal of apoE from the remnant. The LDL receptor-independent remnant-binding site was also present in membranes prepared from isolated hepatocytes and had the same characteristics as the site on membranes prepared from whole liver. In contrast, when chylomicron remnants were incubated with a primary culture of rat hepatocytes, the anti-LDL receptor antibody prevented specific cell association by 84% and degradation of chylomicron remnants completely. Based on these studies, we conclude that although binding of chylomicron remnants to liver cell membranes is not dependent on the LDL receptor, their intact uptake by hepatocytes is.     

Immunochemical characterization of the human blood cell membrane glycoprotein recognized by the monoclonal antibody 12E7.

The 12E7 murine monoclonal antibody recognizes a protease-sensitive component of human red cells, platelets and lymphocytes which could not be detected on granulocytes. Scatchard analyses indicated that the 125I-labelled antibody binds to 1000, 4000 and 27,000 antigen sites on each red cell, platelet and lymphocyte respectively, with a binding constant ranging from 4 x 10(7) to 9 x 10(7) M-1. The membrane components recognized by the monoclonal antibody were characterized by immunostaining on nitrocellulose sheets. A 28 kDa sialoglycoprotein was visualized following electrophoretic transfer of the red cell and lymphocyte membrane proteins separated by SDS/polyacrylamide-gel electrophoresis. Another component of 25 kDa was also clearly identified in the lymphocyte and platelet lysates, but was barely detectable in the red cell membrane preparations. Enzyme treatment of intact platelets, as well as analysis of the membrane and cytosolic preparations from these cells, have shown that the 25 kDa component was of cytoplasmic origin. The mobility of the 28 kDa membrane component is decreased following neuraminidase treatment of intact blood cells, but these cells still react normally with the monoclonal antibody, indicating that sialic acids are not required for binding. The 28 kDa component is present on red cell membranes prepared from S-s-U-, En(a-) and Gerbich(-) individuals, demonstrating that it is a new sialoglycoprotein not derived from glycophorins A, B, C or D. The 28 kDa component was totally solubilized with 0.1% Triton X-100 from red cell membranes and behaves like the other red cell membrane sialoglycoproteins since it was extracted in the aqueous phase following chloroform/methanol/water or butanol/water partitionings. The 28 kDa component could be partially purified by h.p.l.c. gel permeation chromatography and preparative SDS/polyacrylamide-gel electrophoresis. The material finally obtained strongly inhibits the 12E7 monoclonal as well as human anti-Xga antibodies, suggesting either that the 28 kDa glycoprotein carries both antigens or that the 12E7 and Xga-active molecules copurified.     

Production and characterization of antibody blocking epidermal growth factor:receptor interactions

Membranes were prepared from the human epithelioid carcinoma cell line A-431 which has approx. 2 . 10(6) epidermal growth factor receptors per cell. This membrane preparation which retained a high epidermal growth factor binding specific activity was used as an antigen to produce antisera in rabbits. Double-immunodiffusion experiments demonstrated that the immune serum contained precipitating antibodies to several components of detergent solubilized A-431 membranes. The immunoglobulin G fraction of this immune sera inhibited 125I-labeled epidermal growth factor binding to receptors in: (1) intact human and mouse cells; (2) membrane preparations from A-431 cells and human placenta, and (3) solubilized A-431 membranes. Inhibition of 125I-labeled epidermal growth factor binding was observed with divalent and monovalent fragments of immunoglobulin G prepared from the immunoglobulin G fraction. Also, the immunoglobulin G fraction blocked growth factor binding to membranes at low temperature (5 degrees C). Anti-A-431 antibody blocked the induction of DNA synthesis in quiescent fibroblasts by epidermal growth factor in a manner similar to that of anti-epidermal growth factor antibody. Addition of either anti-A431 or anti-epidermal growth factor antibodies to fibroblasts at times up to 5 h after the addition of epidermal growth factor completely reversed the hormone's mitogenic potential. At later times (after 12 h) addition of either antibody was without effect on the stimulation of DNA synthesis by epidermal growth factor. Anti-A-431 antibody did not block the induction of DNA synthesis in fibroblasts by fibroblast growth factor or serum.     

High-frequency antigens of human erythrocyte membrane sialoglycoproteins, IV. Molecular properties of the U antigen

The nature of the common erythrocyte antigen U, that is absent from S-s-U-cells, which lack glycophorin B (Ss sialoglycoprotein), was investigated using six different antisera. The molecular features of a U-like antigen (Duclos), detected by a hitherto unique serum, were also studied. The U and Duclos antigens are complex in that they exhibit relationships with the MNSs and Rh blood group systems. Various fractionation, cleavage, or modification products of normal erythrocyte membranes were used in hemagglutination inhibition assays. Both, the U and Duclos antigens were found to represent labile structures that require lipids, at least for optimum expression of antigen activity. The antigens could be solubilized using conditions of Triton X-100 extraction that release glycophorin B, but solubilize the Rh antigens only to a small extent. Anti-U and anti-Duclos were also inhibited, albeit weakly, by glycophorin B-containing fractions obtained by chromatographic separation of Triton X-100 extracts. The residues approx. 33-39 of glycophorin B represent essential parts of the U antigen, as judged from proteolytic digestion and chemical modification. Conversely, the expression of Duclos activity seems to require a region of glycophorin B (C-terminal of the positions approx. 34-36) that could not be cleaved by various proteinases. Data obtained with anti-Duclos have to be interpreted with caution, since there is evidence that this serum might contain a mixture of antibodies.     

Studies on the characterization of the Rho(D) antigen.

The Rho(D) antigen of red cell membranes was solubilized using ethylene-diamine tetraacetic acid (EDTA) and 2-mercaptoethanol. The solubilized antigen was partially separated from other solubilized membrane components using molecular filtration. The antigen was treated with various enzymes to learn some of the chemical characteristics. It was found that the activity of the antigen, as measured by hemagglutination inhibition, was not affected by bee venom phospholipase A, Clostridium welchii phospholipase C, calf-intestinal alkaline phosphatase, Vibrio cholerae neuraminidase, pig kidney leucine aminopeptidase, bovine pancreatic carboxypeptidase A, and pig pancreatic carboxypeptidase B. However, the proteolytic enzymes, pronase, trypsin, chymotrypsin and papain, did destroy Rho(D) activity as measured by hemagglutination inhibition. These results indicate that protein is an important part of the active determinant of the Rho(D) antigen. The experiments by other investigators have shown that lipid is important to maintain the Rho(D) activity in the intact membrane; lipid probably helps to maintain the structural conformation of the Rho(D) molecule in its natural environment. The solubilized Rho(D) molecules are apparently not dependent on lipid for their Rho(D) activity.     

Production and characterization of antibody blocking epidermal growth factor: Receptor interactions

Membranes were prepared from the human epithelioid carcinoma cell line A-431 which has approx. 2 · 10⁶ epidermal growth factor receptors per cell. This membrane preparation which retained a high epidermal growth factor binding specific activity was used as an antigen to produce antisera in rabbits. Double-immunodiffusion experiments demonstrated that the immune serum contained precipitating antibodies to several components of detergent solubilized A-431 membranes.The immonoglobulin G fraction of this immune sera inhibited ¹²⁵I-labeled epidermal growth factor binding to receptors in: (1) intact human and mouse cells; (2) membrane preparations from A-431 cells and human placenta, and (3) solubilized A-431 membranes. Inhibition of ¹²⁵I-labeled epidermal growth factor binding was observed with divalent and monovalent fragments of immunoglobulin G prepared from the immunoglobulin G fraction. Also, the immunoglobulin G fraction blocked growth factor binding to membranes at low temperature (5°C).Anti-A-431 antibody blocked the induction of DNA synthesis in quiescent fibroblasts by epidermal growth factor in a manner similar to that of anti-epidermal growth factor antibody. Addition of either anti-A-431 or anti-epidermal growth factor antibodies to fibroblasts at times up to 5 h after the addition of epidermal growth factor completely reversed the hormone's mitogenic potential. At later times (after 12 h) addition of either antibody was without effect on the stimulation of DNA synthesis by epidermal growth factor. Anti-A-431 antibody did not block the induction of DNA synthesis in fibroblasts by fibroblast growth factor or serum.     

Solubilization and characterization of an angiotensin II binding protein from liver

Binding sites with high affinity for angiotensin II were solubilized from hepatic membranes by treatment with digitonin. Binding of radioiodinated angiotensin II was assayed by gel filtration and independently by a technique exploiting the failure of activated charcoal to adsorb the bound ligand. The binding protein was partially purified using ammonium sulfate fractionation followed by gel filtration, and in the presence of protease inhibitors, the isolated binding protein preparation did not catalyze degradation of the angiotensin II. Binding to the membranes as well as to the solubilized preparation was specific and saturable. The membranes exhibited a single set of high-affinity binding sites with a Kd of 0.5 nM. The solubilized preparation, also showed the presence of a single class of high-affinity binding sites (Kd = 10.5 nM). Displacement studies using angiotensin I as well as various fragments, agonists and antagonists of angiotensin II disclosed a structure-activity profile similar to that found with intact membranes. Dissociation of angiotensin II from the soluble macromolecular complex was slow but was enhanced at non-physiological pH values or in the presence of 4.5 M urea, or 1% sodium dodecyl sulfate. Covalent binding of the radioiodinated angiotensin II to a single, specific macromolecular component was achieved by treatment with disuccinimidyl suberate. The apparent molecular weight of this reduced, denatured radioactive protein was estimated at about 68 000 by polyacrylamide gel electrophoresis.     

Developmentally regulated 75-kilodalton protein expressed in LLC-PK1 cultures is a component of the renal Na+/glucose cotransport system

Na+/D-glucose symport is a secondary active glucose transport mechanism expressed only in kidney proximal tubule and in small intestine. A monoclonal antibody that recognized the Na+/glucose symporter of pig renal brush border membranes also recognized a 75-kD protein in apical membranes isolated from highly differentiated LLC-PK1 cultures, an epithelial cell line of pig renal proximal tubule origin. The 75-kD antigen was enriched from solubilized LLC-PK1 apical membranes by means of high-pressure liquid chromatography. The symporter antigen became apparent on the apical membrane surface after the development of a confluent monolayer in correlation with the expression of transport activity. Long-term treatment of cultures with the differentiation inducer hexamethylene bisacetamide was accompanied by a dramatically increased expression of the symporter antigen as detected quantitatively by Western blot analysis and qualitatively by immunofluorescence staining. The number of symporter-positive cells was dramatically increased after inducer treatment as predicted for differentiation-regulated expression. These results identify a 75-kD protein as a component of a developmentally regulated renal Na+/glucose symporter expressed in cell culture.     

Subcellular localization of the Streptococcus mutans P1 protein C terminus.

To determine the subcellular location of the Streptococcus mutans P1 protein C-terminal anchor, cell envelope fractionation experiments were conducted in combination with Western immunoblotting, using monoclonal antibody MAb 6-8C specific for an epitope that maps near the C terminus of P1 protein and also a polyclonal antibody preparation directed against the P1 C-terminal 144 amino acids (P1COOH). P1 protein was detected in cell walls but not the membrane purified from S. mutans cells by the monoclonal antibody. In contrast, P1 protein was not detected in the same cell wall preparation using the anti-P1COOH polyclonal antibody. However, proteins released from the cell walls by treatment with mutanolysin contained antigen that was recognized by the anti-P1COOH antibody, suggesting that the epitopes recognized by the antibody were masked by peptidoglycan in the cell wall preparations. When cell walls were treated with boiling trichloroacetic acid to solubilize cell-wall-associated carbohydrate, P1 antigen could not be detected in either the solubilized carbohydrate, or in the remaining peptidoglycan, regardless of whether polyclonal or monoclonal antibody was used. However, when the peptidoglycan was treated with mutanolysin, P1 antigen could be detected in the mutanolysin solubilized fraction by MAb 6-8C. Collectively, these data suggest that the C-terminal 144 amino acids of the P1 protein are embedded within the cell wall, and associated exclusively with the peptidoglycan. Furthermore, the ability of the anti-P1COOH antibody to recognize P1 antigen only after mutanolysin treatment of cell walls suggests these C-terminal 144 amino acids are tightly intercalated within the peptidoglycan strands.     

Electron microscopic localization of calelectrin, a Mr 36 000 calcium-regulated protein, at the cholinergic electromotor synapse of Torpedo

Calelectrin is a calcium-binding protein of Mr 36 000 which has previously been shown to be associated with membranes of the cholinergic synapse in a calcium-dependent manner. We report here that calelectrin was solubilized from the electric organ of Torpedo marmorata in the absence of calcium together with proteins of Mr 54 000 and Mr 15 000. In cholinergic nerve endings isolated from the electric organ only calelectrin was solubilized in a calcium-dependent manner. A specific antiserum to calelectrin was used to localize the antigen by immunofluorescence microscopy on sections of electric organ and showed that calelectrin is distributed throughout the postsynaptic cell. Calelectrin was also detected in axons and in the cell bodies of the cholinergic neurones where it was concentrated in discrete patches throughout the cells. Electric organ tissue was processed to localize calelectrin with the electron microscope using an immunoperoxidase method. The most intense staining was observed on the cytoplasmic face of the acetylcholine receptor-containing postsynaptic membrane and also associated with the intracellular filaments of the electrocyte. The intensity of staining associated with these structures could be greatly reduced by preincubating the tissue with calcium chelators. In nerve terminals calelectrin was associated with synaptic vesicles in a polarized fashion. Calelectrin was also found on the cytoplasmic face of the synaptosomal plasma membrane and associated with neurofilaments. No extracellular staining was ever observed. Our results strongly support our original hypothesis that calelectrin is a calcium-regulated component of intracellular structure associated both with membranes and filaments.     

Multiplicity of molecules carrying blood-group-I antigen on erythrocyte membranes.

A human serum containing a monoclonal anti-(blood-group I) antibody was used to investigate the distribution of blood-group-I antigen on erythrocyte membrane components. Sodium dodecyl sulphate/polyacrylamide-gel-electrophoresis profiles of immuneprecipitates by using 3H-labelled (by the galactose oxidase/NaB3H4 method) and 125I-labelled solubilized stroma were compared. Different radioactive profiles were revealed by the two radiolabelling methods. In the immunoprecipitates the predominant 125I radioactivity within the gel had the electrophoretic mobility of Band-3 protein (apparent mol.wt. 90 000--100 000), whereas the 3H radioactivity revealed a diffusely migrating component(s) (apparent mol.wt. range 40 000--70 000) in addition to radioactivity compatible with glycolipids at the dye front. The diffusely migrating 3H-labelled component was shown to have a similar electrophoretic mobility to a subpopulation of erythrocyte poly(glycosyl)ceramides with blood-group-I activity.     

Studies on the characterization of the Rho(D) antigen

The Rh_o(D) antigen of red cell membranes was solubilized using ethylenediamine tetraacetic acid (EDTA) and 2-mercaptoethanol. The solubilized antigen was partially separated from other solubilized membrane components using molecular filtration. The antigen was treated with various enzymes to learn some of the chemical characteristics. It was found that the activity of the antigen, as measured by hemagglutination inhibition, was not affected by bee venom phospholipase A, Clostridium welchii phospholipase C, calf-intestinal alkaline phosphatase, Vibrio cholerae neuraminidase, pig kidney leucine aminopeptidase, bovine pancreatic carboxypeptidase A, a pig pancreatic carboxypeptidase B. However, the proteolytic enzymes, pronase, trypsin, chymotrypsin and papain, did destroy Rh_o(D) activity as measured by hemagglutination inhibition. These results indicate that protein is an important part of the active determinant of the Rh_o(D) antigen. The experiments by other investigators have shown that lipid is important to maintain the Rh_o(D) activity in the intact membrane; lipid probably helps to maintain the structural conformation of the Rh_o(D) molecule in its natural environment. The solubilized Rh_o(D) molecules are apparently not dependent on lipid for their Rh_o(D) activity.     

Identification and partial characterization of the human erythrocyte membrane component(s) that express the antigens of the LW blood-group system.

Rhnull human erythrocytes lack the antigens of the Rhesus blood-group system, have an abnormal shape, have an increased osmotic fragility, and are associated with mild chronic haemolytic anaemia. Rhnull erythrocytes also lack all antigens of the LW blood-group system, but the functional significance of this deficiency is unknown. We have identified, by immunoblotting with two mouse monoclonal antibodies (BS46 and BS56), the LW-active component(s) in normal human erythrocytes as a broad band of Mr 37 000-47 000 on SDS/polyacrylamide-gel electrophoresis. Treatment of intact human erythrocytes with endoglycosidase F preparation destroyed the epitopes recognized by antibodies BS46 and BS56, suggesting that one or more N-glycosidically linked oligosaccharides are required for the formation of the LW antigens. Estimation of the number of LW antigen sites per erythrocyte by using radioiodinated purified antibody BS46 gave average values of 4400 molecules/cell for Rh(D)-positive adult erythrocytes and 2835 molecules/cell for Rh(D)-negative adult erythrocytes. Like the Rh(D) polypeptide, the LW polypeptide(s) is (are) associated with the cytoskeleton of normal erythrocytes. These results suggest the possibility that the absence of the LW polypeptide may also contribute to the functional and/or morphological abnormalities of Rhnull erythrocytes.     

Protein analysis of cardiac sarcolemma: effects of membrane-perturbing agents on membrane proteins and calcium transport.

Protein composition of cardiac sarcolemmal membranes was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Membranes were observed to contain about 20 polypeptide bands ranging from 18000 to 200 000 dalton mass. Out of these, six bands were prominent and together comprised 57% of the membrane protein. When sarcolemmal membranes, phosphorylated by [gamma-(32)P] ATP in the presence of Ca(2+) or Na+ with and without K+, were fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis at pH 2.4, the band III region (Mr 105 000) of gels was found to contain active sites of monomeric Ca-ATPase and (Na,K)ATPase. Bands I (Mr greater than 200 000), II (Mr 150 000), III (Mr 105 000), and VI (Mr 47 000) were accesible to trypsin; the extent of proteolysis was dependent on the time of exposure to, and the concentration of, trypsin (i.e, ratio of sarcolemmal protein/trypsin). Addition of molar sucrose protected sarcolemmal proteins from the tryptic proteolysis. Calcium transport was reduced by the action of trypsin; the degree of reduction was influenced by the time of exposure of membranes to trypsin as well as the concentration of trypsin. (Mg,Ca)ATPase activity, on the other hand, was elevated moderately at lower concentration and reduced at higher concentration of trypsin. Treatment with phospholipase C cium transport and (Mg,Ca)ATPase activity; electrophoretic patterns were unaffected by this treatment. Addition of lecithin to phospholipase C treated membranes produced a moderate increase in calcium transport. Exposure to Triton X-100 (1%) specifically solubilized three protein bands (Mr90 000, 67 000, and 57 000), whereas exposure to deoxycholate (1%) preferentially solubilized high-molecular-weight proteins, including band III (Mr 105 000); Lubrol-PX (1%) caused nonspecific solubilization of proteins, although the extent of solubilization with Lubrol-PX was considerably less than with either Triton or deoxycholate.     

Purification and partial characterization of the Mr 30,000 integral membrane protein associated with the erythrocyte Rh(D) antigen

Erythrocytes bearing the Rh(D) antigen have an Mr 30,000 integral membrane protein which can be surface-labeled with 125I and can be quantitatively immunoprecipitated from Triton X-100-solubilized spectrin-depleted membrane vesicles. The 125I-labeled Rh(D)-associated protein was purified to radiochemical homogeneity from membrane skeletons solubilized in sodium dodecyl sulfate and urea by hydroxylapatite chromatography, gel filtration, and preparative polyacrylamide gel electrophoresis. The Rh(D)-associated protein was purified nearly 200-fold from 2 units of erythrocytes from DD individuals by employing similar methods on a large scale using the purified 125I-labeled Rh(D)-associated protein as a tracer. The product appeared to be greater than 95% pure and migrated as a diffuse band of Mr approximately 30,000-32,000 on silver-stained sodium dodecyl sulfate electrophoresis gels poured from 12% acrylamide. It is estimated that the Rh(D)-associated protein makes up approximately 0.5% of the original membrane protein. When concentrated, partially purified Rh(D)-associated protein forms dimers and larger oligomers which are stable in sodium dodecyl sulfate and urea. The Rh(D)-associated protein was protected from degradation when intact erythrocytes or inside out membrane vesicles were enzymatically digested. These studies indicate that the Mr 30,000 protein associated with the Rh(D) antigen is linked to the membrane skeleton, resides within the lipid bilayer with minimal extra- or intracellular protrusions, exists normally as an oligomer, and can be purified in denatured form.     

Novel tumor-associated antigen of hepatocellular carcinoma defined by monoclonal antibody E4-65

A monoclonal antibody, E4-65, produced by immunizing mice with SMMC-7721 cells, a human hepatocellular carcinoma (HCC) cell line, was used to identify and characterize an unreported HCC-associated antigen. Indirect immunofluorescence studies showed that E4-65 antibody reacted with five out of eight HCC cell lines, but not with 10 non-HCC tumor cell lines or a normal liver cell line. Using immunohistochemical examination, E4-65 antigen was detected on the cell membranes and in the cytoplasm of human liver tumor tissues, but was not found in most other tumors, or normal adult or fetal tissues, except for a weakly positive reaction in tissues of the digestive system. Western blot analysis showed that E4-65 antibody bound to a 45 kDa protein in the human HCC cell line and tissue lysates. Enzyme treatment and lectin blotting did not detect the carbohydrate chain in E4-65 antigen. This HCC-associated protein represents a potentially useful target for diagnoses and immunotherapy of human HCC.     

Use of a monoclonal antibody to evaluate integrity of the plasma membrane of stallion sperm

Transmission electron microscopy was used to confirm that a monoclonal antibody (F79.3E2; class IgGlK) was specifically localized to an antigen in the acrosomal ground substance of stallion sperm. This antibody was used to develop and validate an indirect immunofluorescent procedure to evaluate integrity of the plasma-acrosomal membranes of stallion sperm. The concept was that primary monoclonal antibody would be “shielded” from its acrosomal antigen by an intact plasma membrane. Conversely, sperm with damaged plasma-acrosomal membranes would exhibit green acrosomal fluorescence when viewed with an epifluorescence microscope. A lipophilic counterstain (red fluorescence) was used to insure that all sperm were visualized. Sperm in fresh-extended or frozen-thawed semen were incubated with hybridoma supernatant containing monoclonal antibody for 30 min at 37°C, then a second antibody (rabbit anti-mouse IgG-FITC) was added for 30 min at 37°C. Unbound antibody was removed by dilution and centrifugation. Sperm were resuspended in phosphate-buffered saline containing Evan's blue as a counterstain. All sperm fluoresced bright red, regardless of the status of cell membranes, except that in cells with damaged plasma-acrosomal membranes, the green fluorescence associated with antibody was overriding for the rostral portion. By counting fluorescent and nonflourescent “acrosomes”, the percentage of sperm with intact plasma-acrosomal membranes was easily determined. Evaluation of five mixtures of undamaged and damaged sperm by this procedure gave a correlation of 0.91 between the percentage of damaged sperm in a mixture and the percentage of sperm with a fluorescent acrosome. Intra- and interassay coefficients of variability were < 6%.